Interferons are proteins having a variety of biological activities, some of which are antiviral, immunomodulating and antiproliferative. They are relatively small, species-specific, single chain polypeptides, produced by mammalian cells in response to exposure to a variety of inducers such as viruses, polypeptides, mitogens and the like. Interferons protect animal tissues and cells against viral attack and are an important host defense mechanism. In most cases, interferons provide better protection to tissues and cells of the kind from which they have been produced than to other types of tissues and cells, indicating that human-derived interferon should be more efficacious in treating human diseases than interferons from other species.
There are several distinct types of human interferons, generally classified as leukocyte (interferon-alpha), fibroblast (interferon-beta) and immune (interferon-gamma), and a large number of variants thereof. General discussions of interferons can be found in various texts and monographs including: The Interferon System (W. E. Stewart, II, Springer-Verlag, N.Y. 1979); and Interferon Therapy (World Health Organization Technical Reports Series 676, World Health Organization, Geneva 1982), incorporated herein by reference.
The method of administering interferon is an important factor in the clinical application of this important therapeutic agent. Systemic administration of interferon by either intravenous, intramuscular or subcutaneous injection has been most frequently used with some success in treating disorders such as hairy cell leukemia, Acquired Immune Deficiency Syndrome (AIDS) and related Kaposi's sarcoma. It is known, however, that proteins in their purified form are especially susceptible to degradation. For interferon-beta, the primary mechanism(s) of interferon degradation in solution are aggregation and deamidation. The lack of interferon stability in solutions and other products has heretofore limited its utility.
Pharmaceutical interferon compositions for clinical use commonly contain interferon as a lyophilized (i.e., freeze-dried) preparation in combination with complex organic excipients and stabilizers such as nonionic surface active agents (i.e., surfactants), various sugars, organic polyois and/or human serum albumin. Lyophilized preparations have the disadvantage of requiring complex packaging since a separate supply of sterile water for injection is required. Moreover, lyophilized preparations require several manipulations prior to use, thus increasing the possibility of needle sticks and dropped components during preparation for injection. These manipulations are especially problematic for patient populations that exhibit muscle weakness and poor coordination, such as people with multiple sclerosis (MS). MS patients may self-administer interferons so that the availability of a dosage form that is much easier to administer than current lyophilized products represents important added value for the target patient population. Simple liquid formulations of interferon are highly desirable in order to avoid the reconstitution necessary when lyophilized preparations are used.
Liquid, non-lyophilized formulations containing interferons may also contain complex carriers such as human serum albumin, polyols, sugars, and anionic surface active stabilizing agents. See, for example, WO 89/10756 (Hara et al.—containing polyol and p-hydroxybenzoate).